The animal viruses provide technically convenient lipid membrane systems with medically interesting surface glycoprotein activities, for the study of basic protein lipid and protein-carbohydrate interactions. This proposal outlines the three dimensional X-ray crystallographic structure determination of the major surface antigen, the hemagglutinin glycoprotein, of influenza virus, along with electron microscopic and biochemical characterizations of its hydrophobic "tail" peptide. The hemagglutinin is the most suitable glycoprotein for the structural studies proposed, and the opportunity for understanding its functions in viral maturation by budding, and host cell binding and membrane penetration at infection. Furthermore, biannual influenza epidemics and occasional pandemics results from the hemagglutitin's ability to undergo marked antigenic variations (drifts and shifts) while preserving its biological activity. Knowledge of the three-dimensional structure of the hemagglintinin should reveal the basis for this evolutionarily and medically significant process. We further propose preliminary experiments designed to produce a direct visualization of antigen-antibody recognition by structural studies of a nomoclonal Fab-Hemagglutinin interaction. This proposal also outlines continuing biochemical characterization of the Sendai virus fusion protein active in cell membrane fusion events and viral penetration.